翻譯名義集 3.259

3.259

【蔡】《指歸》云：「那爛陀僧吉祥月云：『西域立表量影。』影，梵云蔡。此云影，朝蔡倒西去，便以脚足前後步之，數足步影也。」新《毘柰耶》云：「佛言：『應作商矩法。取細籌長二尺許，折一頭四指，竪至日中，度影長短，是謂商矩。』」一說商矩二尺，屈折頭轉，如人脚影，故人濫用。

[Chāyā]: The Zhigui states: 'The monk Auspicious Moon of Nālandā says: "In the Western Regions they erect a gnomon to measure shadows." Shadow is called chāyā in Sanskrit. Here translated as shadow. In the morning, as the shadow falls westward, one paces it out heel to toe, counting the foot-paces of the shadow.' The new Vinaya states: 'The Buddha said: "You should perform the method of the śaṅku. Take a slender stick about two chi long, bend one end by four fingers, set it upright at midday, and measure the length of the shadow: this is called the śaṅku." One explanation says that the śaṅku is two chi long, bent and turned at the end like the shadow of a human foot, which is why people confuse its use.'